Decoding apparatus and method of optical information reproducing system

ABSTRACT

The invention discloses a decoding apparatus and the method thereof for decoding a signal retrieved by an optical information reproducing system from an optical information recording medium. N legal codes are predetermined. According to the invention, first, the retrieved signal is converted into a data stream. Then, in a Viterbi decoding manner, the data stream is decoded into a digital code in accordance with a level of the data stream and N reference levels. Then, the binary code is decoded by a binary array into one of the N legal codes, and each of the N legal codes corresponds to one of N reference levels. In particular, the N reference levels are corrected by various detected conditions to enhance the correctness of decoded data.

BACKGROUND OF THE INVENTION

1. Field of the invention

The invention relates to a decoding apparatus and the method thereof ofan optical information reproducing system, and more particularly to adecoding apparatus and the method thereof utilizing Viterbi decoding.

2. Description of the prior art

Referring to FIG. 1, FIG. 1 is a schematic diagram illustrating adecoding apparatus 10 of a conventional optical information reproducingsystem (e.g. CD-ROM drive). The decoding apparatus 10 includes anequalizer 12, a Viterbi decoder 14, a demultiplexer 16, a binary array18, a delay 20, and a reference level generating device 22.

The equalizer 12 is used for receiving a radio frequency signal FRF andoutputting an equalization signal Feq with respect to the signal FRF,wherein the signal FRF is related to a pickup head (not shown)retrieving a data (not shown) from an optical information recordingmedium (not shown), e.g. compact disc. According to a reference levelRL, the Viterbi decoder 14 decodes the equalization signal Feq to adigital signal Fbi and outputs the digital signal Fbi. The binary array18 is used for receiving the feedback of the digital signal Fbi. Thedelay 20 is used for receiving the feedback of the equalization signalFeq. The demultiplexer 16 is used for respectively receiving the outputsfrom the binary array 18 and the delay 20, and, according to the outputof the binary array 18, selectively inputting the output of the delay 20into a corresponding low-pass filter 222 of the reference levelgenerating device 22. Afterward, the reference level generating device22 will generate the reference level RL.

In the decoding apparatus 10 of the conventional optical informationreproducing system, once the optical information recording medium (e.g.CD) is damaged, such as scratch, finger print, etc. The data stored inthe damaged area and read by the pickup head are incorrect data.Accordingly, the reference level generating apparatus 22 will generatean incorrect reference level RL, so that the Viterbi decoder 14 willdecode the data to incorrect information.

Moreover, in the decoding apparatus 10 of the conventional opticalinformation reproducing system, N calculators are needed to calculate Nreference levels. In other words, it had not been seen in the prior artabout that sharing less than N calculators to calculate N referencelevels.

SUMMARY OF THE INVENTION

An objective of the invention is to provide a decoding apparatus and themethod thereof for an optical information reproducing system, so as tosolve the above-mentioned problems.

Another objective of the invention is to provide a decoding apparatusand the decoding method thereof for an optical information reproducingsystem, and in particular, the invention utilizes M calculators tocalculate N reference levels, wherein N and M both are a natural numberand M is less than N.

According to a preferred embodiment of the invention, the decodingapparatus is used for decoding a signal retrieved by an opticalinformation reproducing system from an optical information recordingmedium. N legal codes are predetermined, wherein N is a natural number.The decoding apparatus includes an Analog-to-digital converter (ADC), anequalizer, a Viterbi decoder, a delay device, a reference leveladjusting device, a conversion-speed-adjusting coefficient generatingdevice, and at least one condition detector. The ADC is used forconverting the retrieved signal into a data stream. The equalizer iscoupled to an output of the ADC and used for outputting an equalizeddata stream corresponding to the data stream. The Viterbi decoder iscoupled to an output of the equalizer and used for decoding, accordingto N reference levels and a level of the equalized data stream, theequalized data stream into the original data stored in the opticalmedium, wherein each of the N reference levels corresponds to one of theN legal codes. The binary array is used for decoding the digital datadecoded by the Viterbi decoder into one of the N legal codes. The delaydevice is coupled to the output of the equalizer and used for delayingthe equalized data stream. The reference level adjusting device isrespectively coupled to an output of the binary array and an output ofthe delay device. The reference level adjusting device is used forreceiving the code relative to the data stream and the equalized datastream corresponding to the code relative to the data stream. Thereference level adjusting device is further used for adjusting the Nreference levels in accordance with an algorithm including aconversion-speed-adjusting coefficient and for outputting the Nreference levels to the Viterbi decoder. The conversion-speed-adjustingcoefficient generating device is used for generating theconversion-speed-adjusting coefficient in response to at least onecondition signal and for outputting the conversion-speed-adjustingcoefficient to the reference level adjusting device. Each of the atleast one condition detector is in charge of detecting a respectivecondition associated with the retrieved signal and outputs one of the atleast one condition signal corresponding to the detected condition tothe conversion-speed-adjusting coefficient generating device.Furthermore, the equalizer may be omitted in practical application, buta little performance will be sacrificed.

According to a preferred embodiment of the invention, the decodingmethod is used for decoding a signal retrieved by an optical informationreproducing system from an optical information recording medium. N legalcodes are predetermined, wherein N is a natural number. The decodingmethod includes the steps of: (1) converting the retrieved signal into adata stream; (2) in a Viterbi decoding manner, decoding, according to Nreference levels and a level of the data stream, the data stream intothe original data stored in the optical medium, wherein each of the Nreference levels corresponds to one of N legal codes; (3) detecting atleast one condition and outputting one of at least one condition signalcorresponding to the detected condition; (4) generating aconversion-speed-adjusting coefficient in response to the outputtedcondition signal; and (5) feeding back the code relative to the datastream and the delayed data stream corresponding to the code of the datastream, and adjusting the N reference levels in accordance with analgorithm including the conversion-speed-adjusting coefficient.

BRIEF DESCRIPTION OF THE APPENDED DRAWINGS

FIG. 1 is a schematic diagram illustrating a decoding apparatus of aconventional optical information reproducing system.

FIG. 2 is a schematic diagram illustrating a decoding apparatusaccording to a preferred embodiment of the invention.

FIG. 3 is a diagram illustrating the retrieved signal F_(RS) beingconverted into a data stream by the ADC.

FIG. 4 is a diagram illustrating the trellis diagram of the Viterbidecoder.

FIG. 5 is a schematic diagram illustrating the waveform of a defectsignal.

FIG. 6 is a schematic diagram illustrating the waveform of a blanksignal.

FIG. 7 is a schematic diagram illustrating the waveform of a scratchsignal.

FIG. 8 is a schematic diagram illustrating the PLL shown in FIG. 2.

FIG. 9 is a schematic diagram illustrating the detailed structure of thereference level adjusting device according to a preferred embodiment ofthe invention.

FIG. 10 is a schematic diagram illustrating how the reference levelcalculator works when the number of the reference level calculator isequal to 1.

FIG. 11 is a schematic diagram illustrating the detailed structure ofthe reference level adjusting device according to another preferredembodiment of the invention.

FIG. 12 is a flowchart illustrating the decoding method according to apreferred embodiment of the invention.

FIG. 13 is a schematic diagram illustrating the source of the referencelevel of the Viterbi decoder when the system is started.

FIG. 14A is a diagram illustrating the levels of the retrieved signalsbeing more diffused.

FIG. 14B is a diagram illustrating the levels of the retrieved signalsbeing more centered.

FIG. 15 is schematic diagram illustrating the apparatus capable ofdetermining the centralization of the reference levels.

FIG. 16 is a functional block diagram illustrating an adaptive equalizerof the prior art.

FIG. 17 is a functional block diagram illustrating a structure capableof protecting the adaptive equalizer.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 2, FIG. 2 is a schematic diagram illustrating adecoding apparatus 30 according to a preferred embodiment of theinvention. The decoding apparatus 30 is used for decoding a signalF_(RS) retrieved by an optical information reproducing system from anoptical information recording medium.

As shown in FIG. 3, a signal F_(RS), retrieved from the opticalinformation recording medium, is converted into a data stream by theADC. The reference levels of the data stream always center on somespecific reference levels. Each of the reference levels corresponds to aset of legal codes. Due to the above-mentioned characteristic, theretrieved signal Fps can be decoded by a Viterbi decoder. As shown inFIG. 4, when the Viterbi decoder decodes the retrieved signal F_(RS),each of the branches of the trellis diagram corresponds to a set oflegal codes. Therefore, each of the branches of the trellis diagram alsocorresponds to a reference level. In practical application, the opticalinformation reproducing system has to get a reference level of theoriginal optical reproducing signal and then inputs the reference levelinto the Viterbi decoder. However, the reference level is usuallyinfluenced by scratch, finger print, and so on. Thus, Viterbi decoderwill get an incorrect reference level. Therefore, the inventiondiscloses a decoding apparatus and the method thereof for an opticalinformation reproducing system, so as to solve the problems of the priorart.

In practical application, the above-mentioned pre-defined legal codesare not always as the above-mentioned embodiment but based on thepartial response targets.

As shown in FIG. 2, the decoding apparatus 30 includes an ADC 32, anequalizer 34, a Viterbi decoder 36, a delay device 38, a majoritydetector 40, a reference level adjusting device 42, aconversion-speed-adjusting coefficient generating device 44, at leastone condition detector, and a binary array 59.

The ADC 32 is used for converting the retrieved signal FRS into a datastream FDS. The equalizer 34 is coupled to an output of the ADC 32 andused for outputting an equalized data stream FFDS corresponding to thedata stream FDS. The Viterbi decoder 36 is coupled to an output of theequalizer 34 and used for decoding, according to N reference levels RSand a level of the equalized data stream FFDS, the equalized data streamFFDS. Afterward, a signal selecting device 56 is used for transmittingthe decoded data F_(data) from the Viterbi decoder 36 to the binaryarray 59. The binary array is used for decoding the digital data decodedby the Viterbi decoder 36 into one of the N legal codes Fc. Each of theN reference levels RS corresponds to one of the N legal codes. In otherwords, the Viterbi decoder 36 compares the level corresponding to thedata stream FFDS with one of the N reference levels RS corresponding tothe legal codes Fc, and then adjusts the reference level RS based on thedifference.

Referring to FIG. 2 again, the delay device 38 is coupled to the outputof the equalizer 34 and used for delaying the equalized data streamFFDS. The reference level adjusting device 42 is respectively coupled toan output of the binary array 59 and an output of the delay device 38.The reference level adjusting device 42 is used for receiving the codeFc relative to the data stream FFDS and the equalized data stream FFDScorresponding to the code Fc relative to the data stream FFDS. Thereference level adjusting device 42 is further used for adjusting the Nreference levels RS in accordance with an algorithm including aconversion-speed-adjusting coefficient C and for outputting the Nreference levels RS to the Viterbi decoder 36.

The algorithm is shown as the following:Y _(i,j) =Y _(i,j-1) +C _(i)×(X _(i,j) −Y _(i,j-1))where i represents an index ranging from 1 to N, Y_(i,j) represents thereference level RS corresponding to the i-th legal code and beingcalculated, Y_(i,j-1) represents the reference level RS corresponding tothe i-th legal code and been calculated, X_(i,j) represents the level ofthe data stream relating to the i-th legal code and being calculated,and C_(i) represents the conversion-speed-adjusting coefficientcorresponding to the i-th legal code. Different coefficient C_(i) can beselected based on different code Fc, and Y_(i,0) is a default referencelevel RS. The algorithm is an embodiment utilizing low-pass filtering,and C_(i) is positively related to the bandwidth of low-pass filtering.

Referring to FIG. 2 again, the Viterbi decoder 36 also outputs amajority signal Fms relative to the code Fc, wherein the majority signalFms represents an accuracy of the decoded data F_(data) outputted by theViterbi decoder 36. The majority detector 40 is coupled to the output ofthe Viterbi decoder 36 and used for receiving the majority signal Fms.When the accuracy of the majority signal Fms is unobvious, the majoritydetector 40 will output a control signal FL responsive to the majoritysignal Fms to the reference level adjusting device 42, so as to controlthe reference level adjusting device 42 not to adjust the correspondingreference level RS. In other words, C_(i) is set as zero, or the valueof C_(i) is reduced temporarily.

The conversion-speed-adjusting coefficient generating device 44 is usedfor generating the conversion-speed-adjusting coefficient Ci in responseto at least one condition signal and for outputting theconversion-speed-adjusting coefficient Ci to the reference leveladjusting device 42. Each of the at least one condition detector is incharge of detecting a respective condition associated with the retrievedsignal FRS and outputs one of the at least one condition signalcorresponding to the detected condition to theconversion-speed-adjusting coefficient generating device 44. In apreferred embodiment, as shown in FIG. 2, the at least one conditiondetector includes one selected from the group consisting of a defectcondition detector 46, a blank condition detector 48, a scratchcondition detector 50, a training sequence condition detector 52, aservo condition detector 54, and a Phase-locked loop (PLL) conditiondetector 58.

Referring to FIG. 2 and FIG. 5, FIG. 5 is a schematic diagramillustrating the waveform of a defect signal FDS detected by the defectcondition detector 46 shown in FIG. 2. The above-mentioned defectcondition, such as scratch, represents the data stored in the opticalinformation recording medium cannot be identified at all. The defectcondition detector 46 predetermines a first range and has an input forreceiving the signal FDS. When the received signal FDS is lower than thelower limit of the first range, the defect condition detector 46 willoutput a defect condition signal FD. The conversion-speed-adjustingcoefficient generating device 44 will respond to the defect conditionsignal FD and output a minimum or zero as the conversion-speed-adjustingcoefficient C. Then, a default reference level enabling device 60responds to the defect condition signal FD and, based on a user setting,selectively loads a default reference level. Afterward, when thereceived signal FDS is higher than the upper limit of the first range,the defect condition detector 46 will output a defect condition liftedsignal FDL. The conversion-speed-adjusting coefficient generating device44 will respond to the defect condition lifted signal FDL and output theconversion-speed-adjusting coefficient Ci, such as [0.5, 0.5, . . .0.5], representing a default value. Then, the default reference levelenabling device 60 responds to the defect condition lifted signal FDLand, based on the user setting, selectively loads a default referencelevel to converge to a target value or does not loads the initial valueto converge to the target value.

Referring to FIG. 2 and FIG. 6, FIG. 6 is a schematic diagramillustrating the waveform of a blank signal detected by the blankcondition detector 48 shown in FIG. 2. Similar to the above-mentionedoperation of the defect condition detector 46, the blank conditiondetector 48 predetermines a second range for the blank condition. Theblank condition represents the blank area on the optical informationrecording medium. The blank condition detector 48 has an input forreceiving FDS. When the current FDS is higher than the upper limit ofthe second range, the blank condition detector 48 will output a blankcondition signal Fb. The conversion-speed-adjusting coefficientgenerating device 44 will respond to the blank condition lifted signalFb and output the conversion-speed-adjusting coefficient Ci representingzero. Then, the default reference level enabling device 60 responds tothe blank condition signal Fb and, based on the user setting,selectively loads a default reference level (load_ini). Afterward, whenthe signal FDS is lower than the lower limit of the second range, theblank condition detector 48 will output a blank condition lifted signalFbi. The conversion-speed-adjusting coefficient generating device 44will respond to the blank condition lifted signal Fbi and output theconversion-speed-adjusting coefficient Ci representing the defaultvalue. Then, the default reference level enabling device 60 responds tothe blank condition lifted signal Fbi and, based on the user setting,selectively loads a default reference level to converge to a targetvalue or does not loads the initial value to converge to the targetvalue.

Referring to FIG. 2 and FIG. 7, FIG. 7 is a schematic diagramillustrating the waveform of a scratch signal detected by the scratchcondition detector 50 shown in FIG. 2. The scratch condition representsthe data stored in the optical information recording medium is damagedbut still can be identified, e.g. finger print, slight scratch, and soon. The scratch condition detector 50 predetermines a third range forthe scratch condition. The scratch condition detector 50 has an inputfor receiving a data stream FDS. When the variation of the received datastream FDS exceeds the third range during a predetermined span of timeT, the scratch condition detector 50 will output a scratch conditionsignal Fs. The conversion-speed-adjusting coefficient generating device44 will respond to the scratch condition lifted signal Fs and output theconversion-speed-adjusting coefficient Ci larger than the default value.Then, the default reference level enabling device 60 responds to thescratch condition signal Fs, based on the user setting, selectivelyloads a default reference level, and maintains the initial value untilthe scratch condition is lifted. Afterward, when the variation of thereceived data stream FDS varies within the third range during thepredetermined span of time T, the scratch condition detector 50 willoutput a scratch condition lifted signal Fsl. Theconversion-speed-adjusting coefficient generating device 44 will respondto the scratch condition lifted signal Fsl and output theconversion-speed-adjusting coefficient Ci representing the defaultvalue. Then, the default reference level enabling device 60 responds tothe scratch condition lifted signal Fsl and, based on the user setting,selectively loads a default reference level to converge to a targetvalue or does not loads the initial value to converge to the targetvalue.

Referring to FIG. 2, when the signal FRS retrieved by the opticalinformation reproducing system is a training sequence, the trainingsequence condition detector 52 detects whether the decoded data F_(data)outputted from the Viterbi decoder is a training sequence, and thenoutputs a training sequence condition signal Fts. Because the trainingsequence is a known sequence, the training sequence condition detector52 can output a self-generated training sequence Ft to a signalselecting device 56. Then, the conversion-speed-adjusting coefficientgenerating device 44 will respond to the training sequence conditionsignal Fts and output the conversion-speed-adjusting coefficient Cilarger than the default value. Afterward, when the training sequencedoes not appear any more, the training sequence condition detector 52will output a training sequence condition lifted signal Ftsl. Theconversion-speed-adjusting coefficient generating device 44 will respondto the training sequence condition lifted signal Ftsl and output theconversion-speed-adjusting coefficient Ci representing the defaultvalue.

In a preferred embodiment, the training sequence condition detector 52provides the training sequence Ft to the signal selecting device 56.Before receiving the training sequence Ft, the signal selecting device56 is used for receiving the decoded data F_(data) and outputting thecode Fc to the reference level adjusting device 42. When the trainingsequence condition detector 52 receives the training sequence, thesignal selecting device 56 is notified to output a training sequence Ftgenerated by the training sequence condition detector 52 to thereference level adjusting device 42. In another preferred embodiment,when the training sequence condition detector 52 detects there is notany training condition and does not output the training sequence Ft tothe signal selecting device 56, the signal selecting device 56 willselect the decoded data F_(data) as the input. At the same time, thetraining sequence condition detector 52 outputs the training sequencecondition signal Fts to notify the the conversion-speed-adjustingcoefficient generating device 44 to output theconversion-speed-adjusting coefficient Ci larger than the default value.Afterward, when training sequence does not appear any more, the trainingsequence condition detector 52 will output a training sequence conditionlifted signal Ftsl. The conversion-speed-adjusting coefficientgenerating device 44 will respond to the training sequence conditionlifted signal Ftsl and output the conversion-speed-adjusting coefficientCi representing the default value.

Referring to FIG. 2, the servo condition detector 54 is used fordetecting whether the signal F_(RS) retrieved by the optical informationreproducing system is at a track status. When the optical informationreproducing system begins to track the optical information recordingmedium, the servo condition detector 54 will output a track beginningsignal Ftb. The conversion-speed-adjusting coefficient generating device44 will respond to the track beginning signal Ftb and output theconversion-speed-adjusting coefficient Ci representing zero. Then, thedefault reference level enabling device 60 responds to the trackbeginning signal Ftb, based on the user setting, selectively loads adefault reference level, and maintains the initial value until thecondition is lifted. Afterward, when the optical information reproducingsystem stops to track the optical information recording medium, theservo condition detector 54 will output a track end signal Fte. Theconversion-speed-adjusting coefficient generating device 44 will respondto the track end signal Fte and output the conversion-speed-adjustingcoefficient Ci representing the default value. Then, the defaultreference level enabling device 60 responds to the track end signal Fteand, based on the user setting, selectively loads a default referencelevel to converge to a target value or does not loads the initial valueto converge to the target value.

Referring to FIG. 8, FIG. 8 is a schematic diagram illustrating the PLL58 shown in FIG. 2. The PLL 58 includes a sync detector 582. The syncdetector 582 is used for detecting the distance between each frame syncbit of the adjusted data stream FFDS. A reset counter 584 is used fordriving a standard value 586. A comparator 587 is used for judgingwhether the distance between each frame sync bit detected by the syncdetector 582 conforms to the standard value, so as to determine whetherthe PLL is locked. If the PLL is not locked, a phase-locked setting 588will output zero or a minimum as the conversion-speed-adjustingcoefficient, based on the user setting, selectively loads a defaultreference level, and maintains the initial value until the condition islifted. If the PLL is locked, the default conversion-speed-adjustingcoefficient will be outputted.

As shown in FIG. 2, the decoding apparatus 30 further includes a slicer35, a multiplexer 41, an area type detector 43, and a memory 45 forstoring a reference level corresponding to a second type of the area.

The slicer 35 is coupled to the output of the equalizer 34 and used forconverting the adjusted data stream FFDS into a binary data. The slicer35 transmits the binary signal to the signal selecting device 56. Inpractical application, if a disc has a lower recording density, becausethe accuracy of the slicer to decode data is credible, the signalselecting device 56 can selectively replace the decoded data F_(data) bythe binary sugnal. The delay time of the slicer is smaller than theViterbi decoder, so the delay time of the delay device 38 can bereduced.

Because there are always some areas different from the data area on theoptical information recording medium, e.g. header area, thecharacteristic of the reference level of the signal RF in theabove-mentioned area is different from the reference level of the dataarea. Therefore, the memory 45 stores the reference levels correspondingto various types of area (not data area), such as the reference levelcorresponding to the header area. As shown in FIG. 2, the multiplexer 41is connected between the Viterbi decoder 36 and the reference leveladjusting device 42. The area type detector 43 is used for determiningthe signal FRS corresponds to which type of area on the opticalinformation recording medium, and then for outputting a determiningsignal to the multiplexer 41. According to different type of area, themultiplexer 41 selects the reference level from the reference leveladjusting device 42 or the memory 45 and then provides the selectedreference level to the Viterbi decoder 36. Therefore, higher accuracycan be obtained in the header area. Ci of the conversion-speed-adjustingcoefficient generating device is set as zero or other default value.

Referring to FIG. 9, FIG. 9 is a schematic diagram illustrating thedetailed structure of the reference level adjusting device 42 accordingto a preferred embodiment of the invention. The reference leveladjusting device 42 includes M reference level calculators 422, a memory424 for storing N reference levels RS, and a multiplexer 428. At start,the code Fc is transmitted to the multiplexer 428, and then the Nreference levels RS stored in the memory 424 is also transmitted to themultiplexer 428. According to the received code Fc, the multiplexer 428selects one from the N reference levels RS corresponding to the code Fcand transmits the selected reference level RS to the M reference levelcalculators 422. The M reference level calculators 422 receive theequalized signal FFDS and the conversion-speed-adjusting coefficient Ci,so as to calculate the reference level selected by the multiplexer 428and store the calculating result in the memory 424. More particularly, Mis a nature number and smaller than N. Compared to the prior art, theinvention only utilizes M calculators to calculate N reference levels.In practical application, M can be designed as 1, as shown in FIG. 10.The operating method of FIG. 10 includes the following steps: (1)according to the code Fc, selecting one from the N reference levelsstored in the memory 424 to be adjusted; (2) inputting the selectedreference level to a reference level calculator 422; (3) according to analgorithm including a conversion-speed-adjusting coefficient Ci,adjusting the reference level RS; and (4) storing the adjusted referencelevel RS in the memory 424.

In another preferred embodiment, as shown in FIG. 11, the referencelevel adjusting device 42 consists of a plurality of low-pass filters421. Each of the low-pass filters 421 corresponds to one reference levelRS. As shown in FIG. 11, the low-pass filters are controlled by alow-pass filter enabling controller 423 to enable, based on the code Fc,the low-pass filters 421 of the corresponding reference level. Accordingto the conversion-speed-adjusting coefficient Ci, the reference leveladjusting device 42 sets the bandwidth of each low-pass filter and thenfilters the adjusted data stream FFDS, so as to generate the referencelevel RS.0

In the prior art, once the disc is damaged, e.g. scratch, finger print,and so on, the reference level generating device 22 will generate anincorrect reference level, so that the Viterbi decoder 14 will generateincorrect data. Therefore, the invention discloses a decoding apparatus30 capable of correcting the reference level. By utilizing the referencelevel adjusting device 42, the conversion-speed-adjusting coefficientgenerating device 44, the at least one condition detector, and thealgorithm, even though the signal FRS retrieved by the opticalinformation reproducing system from the optical recording medium isincorrect, the invention can still adjust the conversion-speed-adjustingcoefficient Ci to make the reference level adjusting device 42 outputthe reference level towards the correct value, such that the Viterbidecoder 36 can generate the decoded data F_(data) towards the correctdata. Furthermore, the number of the calculators of the reference leveladjusting device 42 can be less than the number of reference levels, soas to reduce the cost and the chip size.

Referring to FIG. 12, FIG. 12 is a flowchart illustrating the decodingmethod according to a preferred embodiment of the invention. In anoptical information reproducing system, the decoding method is used forperforming decoding of a signal retrieved by the system from an opticalinformation recording medium. N legal codes are predetermined.

According to the decoding method of the invention, at start, step S10 isperformed to convert the retrieved signal into a data stream. Afterward,step S12 is performed. In step S12, in a Viterbi decoding manner, thedata stream is decoded into a digital data Fdata originally stored inthe optical medium, and then the data Fdata is inputted into a binaryarray to generate a legal code Fc. Step S14 is then performed. In stepS14, at least one condition is detected, and one of the at least onecondition signal corresponding to the detected condition is outputted.Step S16 is then performed. In step S16, a conversion-speed-adjustingcoefficient in response to the outputted condition signal is generated.Step S18 is then performed. In step S18, the code relative to the datastream and the delayed data stream corresponding to the code of the datastream are fed back, and the N reference levels are adjusted inaccordance with an algorithm including the conversion-speed-adjustingcoefficient.

In practical application, when a data is decoded, the reference level ofthe reference level adjusting device 42 may be incorrect, so that theViterbi decoder 36 may generate incorrect decoded data. Thus, thereference level adjusting device 42 will not get correct code Fc toobtain the correct reference level. The invention discloses a method tosolve the above-mentioned problem. As shown in FIG. 13, when an opticalinformation producing system is started, a start signal (strat_up) willactivate the multiplexer 41 to select the conventional fixed referencelevel stored in a storing device 62, and then the fixed reference levelis used as the reference level for the Viterbi decoder 36. Therefore,the correct result can be obtained via the Viterbi decoder. At thistime, the above-mentioned nearly correct result Fc is used to adjust thereference level RS of the reference level adjusting device 42. After aspan of time, the reference level adjusting device 42 will get correctreference level RS. At this time, the source of the reference level ofthe Viterbi decoder 36 is changed to the reference level adjustingdevice 42, so as to solve the above-mentioned problem.

The quality of an optical reproducing signal can be estimated by thedistribution of the reference levels. The above has mentioned that theoptical reproducing signals (retrieved signals FRS) always center onsome specific reference levels after being synchronously sampled, asshown in FIG. 3. Referring to FIG. 14A and FIG. 14B, FIG. 14A is adiagram illustrating the levels of the retrieved signals being morediffused. FIG. 14B is a diagram illustrating the levels of the retrievedsignals being more centered. If the signals are more centered, thequality of the signal is better. Thus, the quality of an opticalreproducing signal can be determined by the centralization of thereference levels. The centralization of the reference levels can beobtained by the apparatus shown in FIG. 15. As shown in FIG. 15, theapparatus performs a low-pass filtering on the absolute differencebetween a reference level corresponding to a code Fc1 set by a user andthe corresponding signal. Therefore, the centralization of the referencelevel is obtained, and the centralization of all reference levels can bealso obtained in this manner. The detailed operation of the apparatusincludes the following steps: (1) determining whether the code Fc is thecode Fc1 set by the user; (2) if it is a YES in (1), inputting theabsolute difference between FFDS and the reference level correspondingto the code Fc1 into the low-pass filter; (3) compiling statistics aftera span of time to obtain the centralization of the reference levelcorresponding to the code Fc1.

In practical application, the optical information reproducing systemusually utilizes an adaptive equalizer capable of adjusting thecoefficient to equalize the signal, so as to improve the quality of thesignal. According to the signal and a reference signal, the adaptiveequalizer can adjust the coefficient. The reference signal can begenerated by the code Fc via a training sequence, a slicing decoder, ora Viterbi decoder performing decoding operation. A common adaptiveequalizer is called PR-1221, wherein the relation between the referencesignal and the code Fc is as the following and Fc is assumed as binary:$\begin{matrix}{{{Fc} = \begin{bmatrix}b_{0} & b_{1} & b_{2} & b_{3}\end{bmatrix}},} \\{{\hat{y} = {\left( {{2*{Fc}} - 1} \right) \cdot \begin{bmatrix}1 \\2 \\2 \\1\end{bmatrix}}},}\end{matrix}$Wherein Fc is a digital array, e.g. Fc=[0 1 1 1].

Referring to FIG. 16, FIG. 16 is a functional block diagram illustratingan adaptive equalizer 70 of the prior art. The adaptive equalizer 70includes an equalizing unit 72, a reference signal generating device 74,and a coefficient adaptive circuit 75. The coefficient adaptive circuit75 includes an error calculating unit 76 and a coefficient calculatingunit 78. The equalizing unit 72 is a FIR filter having a plurality ofcoefficients C0(0), C1(0), . . . , CN(0) and capable of generating anequalizing signal yeq. The reference signal generating device 74 canutilize a code Fc to generate a desired signal ŷ, wherein the code Fc isoutputted by a binary array after a training sequence, a slicingdecoder, or a Viterbi decoder performs decoding operation. Afterward,the error calculating unit 76 subtracts the desired signal ŷ from theequalizing signal yeq to generate an error signal e. Finally, theadaptive equalizer 70 utilizes the coefficient calculating unit 78 toperform least mean square (LMS) calculation according to the receivedsignal y and the error signal e, so as to generate a plurality of bettercoefficients C0(1), C1(1), . . . , CN(1). The calculation of theconventional coefficient calculating unit 78 is described as thefollowing equation:C _(j)(k)=C _(j)(k−1)−τ·e(k)·y(k).   Equation 1:

In the above equation 1, r represents a conversion-speed-adjustingcoefficient. Afterward, the coefficients C0(0), C1(0), . . . , CN(0)used by the equalizing unit 72 are replaced by the coefficients C0(1),C1(1), . . . , CN(1). When the above-mentioned process is performedrepeatedly, the error signal e will gradually tend to zero, and then thecoefficients C0, C1, . . . , CN will also tend to steady state. When thecondition changes, the error signal e will be amplified, and thecoefficients will also change obviously, so that the adaptive equalizer70 will, according to the above-mentioned operation, adjust thecoefficients of the equalizing unit 72.

However, the adaptive equalizer also utilizes the Viterbi decoder tocalculate the desired signal ŷ. When there is a defect, scratch, orblank on the disc, the data decoded by the Viterbi decoder will beincorrect, and then the adaptive equalizer will not get correctcoefficient. Therefore, the method applied in the reference leveladjusting device can be also used to protect the adaptive equalizer, asshown in FIG. 17.

1. In an optical information reproducing system, a decoding apparatusfor decoding a signal retrieved by said system from an opticalinformation recording medium, N legal codes being predetermined, whereinN is a natural number, said decoding apparatus comprising: anAnalog-to-digital converter (ADC) for converting the retrieved signalinto a data stream; a Viterbi decoder, coupled to an output of the ADC,for decoding, according to N reference levels and a level of the datastream, the data stream into a digital data, wherein each of the Nreference levels corresponds to one of the N legal codes; a binary arrayfor decoding the digital data decoded by the Viterbi decoder into one ofthe N legal codes; a delay device, coupled to the output of the ADC, fordelaying the data stream, and outputting a delayed data streamcorresponding to the data stream; a reference level adjusting device,respectively coupled to an output of the Viterbi decoder and an outputof the delay device, for receiving the code relative to the data streamand the delayed data stream corresponding to the data stream, adjustingthe N reference levels in accordance with an algorithm including aconversion-speed-adjusting coefficient, and outputting the N referencelevels to the Viterbi decoder; a conversion-speed-adjusting coefficientgenerating device for generating the conversion-speed-adjustingcoefficient in response to at least one condition signal, and outputtingthe conversion-speed-adjusting coefficient to the reference leveladjusting device; and at least one condition detector which each is incharge of detecting a respective condition associated with the retrievedsignal and outputs one of the at least one condition signalcorresponding to the detected condition to theconversion-speed-adjusting coefficient generating device.
 2. Thedecoding apparatus of claim 1, wherein the algorithm is as follows:Y _(i,j) =Y _(i,j-1) +C _(i)×(X _(i,j) −Y _(i,j-1)), where i representsan index ranging from 1 to N, Y_(i,j) represents the reference levelcorresponding to the ith legal code and being calculated, Y_(i,j-1)represents the reference level corresponding to the ith legal code andbeen calculated, X_(i,j) represents the level of the data streamrelating to the ith legal code and being calculated, and C_(i)represents the conversion-speed-adjusting coefficient corresponding tothe ith legal code.
 3. The decoding apparatus of claim 1, wherein thereference level adjusting device comprises a plurality of low-passfilters, the reference level adjusting device sets up a bandwidth ofeach low-pass filter in accordance with the conversion-speed-adjustingcoefficient.
 4. The decoding apparatus of claim 1, wherein the at leastone condition detector comprises one selected from the group consistingof a defect condition detector, a blank condition detector, a scratchcondition detector, a training sequence condition detector, a servocondition detector, and a Phase-locked loop (PLL) condition detector. 5.The decoding apparatus of claim 1, wherein the Viterbi decoder alsooutputs a majority signal relative to the code, said decoding apparatusfurther comprises a majority detector, coupled to the output of theViterbi decoder, for receiving the majority signal, and outputting acontrol signal responsive to the majority signal to the reference leveladjusting device which is operated by the control signal.
 6. Thedecoding apparatus of claim 1, wherein the optical information recordingmedium comprises a first type of area, on which the N legal codes areallowed to be recorded, and a second type of area different from thefirst type of area, said decoding apparatus further comprises a memoryfor storing a default reference level corresponding to the second typeof the area, when the retrieved signal relates to data recorded on thesecond type of area, the reference level adjusting device receives thedefault reference level from the memory to replace the N referencelevels.
 7. The decoding apparatus of claim 1, further comprising asignal selecting device coupled between the Viterbi decoder and thebinary array, when the training sequence condition detector detects thetraining sequence condition, the training sequence condition generates atraining sequence, and outputs the training sequence to the binary arraythrough the signal selecting device to replace the digital data.
 8. Inan optical information reproducing system, a decoding method forperforming decoding of a signal retrieved by said system from an opticalinformation recording medium, N legal codes being predetermined, whereinN is a natural number, said decoding method comprising the steps of:converting the retrieved signal into a data stream; delaying the datastream to generate a delayed data stream corresponding to data stream;in a Viterbi decoding manner, decoding, according to N reference levelsand a level of the data stream, the data stream into a digital data,wherein each of the N reference levels corresponds to one of N legalcodes; decoding, by a binary array, the digital data into one of the Nlegal codes; detecting at least one condition, and outputting one of theat least one condition signal corresponding to the detected condition;generating a conversion-speed-adjusting coefficient in response to theoutputted condition signal; and feeding back the code relative to thedata stream and the delayed data stream corresponding to the code of thedata stream, and adjusting the N reference levels in accordance with analgorithm including the conversion-speed-adjusting coefficient.
 9. Thedecoding method of claim 8, wherein the algorithm is as follows:Y _(i,j) =Y _(i,j-1) +C _(i)×(X _(i,j) −Y _(i,j-1)), where i representsan index ranging from 1 to N, Y_(i,j) represents the reference levelcorresponding to the ith legal code and being calculated, Y_(i,j-1)represents the reference level corresponding to the ith legal code andbeen calculated, X_(i,j) represents the level of the data streamrelating to the ith legal code and being calculated, and C_(i)represents the conversion-speed-adjusting coefficient corresponding tothe ith legal code.
 10. The decoding method of claim 8, wherein in thestep of adjusting the N reference levels, the N reference levels aregenerated by a plurality of low-pass filters, a bandwidth of eachlow-pass filter is set up in accordance with theconversion-speed-adjusting coefficient.
 11. The decoding method of claim8, wherein the leas one condition comprises one selected from the groupconsisting of a defect condition, a blank condition, a scratchcondition, a training sequence condition, a servo condition, and aphase-locked loop(PLL) condition.
 12. The decoding method of claim 8,wherein in the step of decoding, a majority signal relative to the codeis also generated, said decoding method further comprises the step ofgenerating a control signal in response to the majority signal, andwherein the step of adjusting the N reference levels is operated by thecontrol signal.
 13. The decoding method of claim 8, wherein the opticalinformation recording medium comprises a first type of area, on whichthe N legal codes are allowed to be recorded, and a second type of areadifferent from the first type of area, a default reference level beingpreviously provided corresponding to the second type of area, when theretrieved signal relates to data recorded on the second type of area,the default reference level replaces the N reference levels to decodethe data stream into the digital data.
 14. The method of claim 11,wherein when the training sequence condition is detected, a trainingsequence is generated to replace the feed back digital data to adjustthe N reference levels.
 15. In an optical information reproducingsystem, a decoding apparatus for decoding of a signal retrieved by saidsystem from an optical information recording medium, N legal codes beingpredetermined, wherein N is a natural number, said decoding apparatuscomprising: an analog-to-digital converter (ADC) for converting theretrieved signal into a data stream; a Viterbi decoder, coupled to anoutput of the ADC, for decoding the data stream into one of the N legalcodes in accordance with the N reference level and a level of the datastream, wherein each of the N reference levels corresponds to one of Nlegal codes; a slicer, coupled to the output of the ADC, for decodingthe data stream into a digital data; a binary array, for decoding thedigital data decoded by the slicer into one of the N legal codes; adelay device, coupled to the output of the ADC, for delaying the datastream, and then outputting a delayed data stream corresponding to thedata stream; a reference level adjusting device, coupled to an output ofthe slicer and an output of the delay device, for receiving the coderelative to the data stream and the delayed data stream corresponding tothe code of the data stream, adjusting the N reference levels inaccordance with an algorithm including a conversion-speed-adjustingcoefficient, and outputting the N reference levels to the Viterbidecoder; a conversion-speed-adjusting coefficient generating device forgenerating the conversion-speed-adjusting coefficient responsive to atleast one condition signal, and outputting theconversion-speed-adjusting coefficient to the reference level adjustingdevice; and at least one condition detector which each is in charge ofdetecting a respective condition associated with the retrieved signaland outputs one of the at least one condition signal corresponding tothe detected condition to the conversion-speed-adjusting coefficientgenerating device.
 16. The decoding apparatus of claim 15, wherein thealgorithm is as follows:Y _(i,j) =Y _(i,j-1) +C _(i)×(X _(i,j) −Y _(i,j-1)), where i representsan index ranging from 1 to N, Y_(i,j) represents the reference levelcorresponding to the ith legal code and being calculated, Y_(i,j-1)represents the reference level corresponding to the ith legal code andbeen calculated, X_(i,j) represents the level of the data streamrelating to the ith legal code and being calculated, and C_(i)represents the conversion-speed-adjusting coefficient corresponding tothe ith legal code.
 17. In an optical information reproducing system, adecoding apparatus for decoding a signal retrieved by said system froman optical information recording medium, N legal codes beingpredetermined, wherein N is a natural number, said decoding apparatuscomprising: an Analog-to-digital converter (ADC) for converting theretrieved signal into a data stream; a Viterbi decoder, coupled to anoutput of the ADC, for decoding the data stream into a digital data inaccordance with N reference levels and a level of the data stream,wherein each of the N reference levels corresponds to one of the N legalcodes; a binary array for decoding the digital data decoded by theViterbi decoder into one of the N legal codes; a delay device, coupledto the output of the ADC, for delaying the data stream, and thenoutputting a delayed data stream corresponding to the data stream; areference level adjusting device, respectively coupled to an output ofthe Viterbi decoder and an output of the delay device, for receiving thecode relative to the data stream and the delayed data streamcorresponding to the relative code, adjusting the N reference levels inaccordance with an algorithm including a conversion-speed-adjustingcoefficient, and outputting the N reference levels to the Viterbidecoder; wherein the reference level adjusting device comprises Mcalculators for calculating the N reference levels, while M is a naturalnumber less than N.
 18. In an optical information reproducing system, adecoding apparatus for decoding a signal retrieved by said system froman optical information recording medium, N legal codes beingpredetermined, wherein N is a natural number, said decoding apparatuscomprising: an Analog-to-digital converter (ADC) for converting theretrieved signal into a data stream; a Viterbi decoder, coupled to anoutput of the ADC, for decoding, according to N reference levels and alevel of the data stream, the data stream into a digital data, whereineach of the N reference levels corresponds to one of N legal codes; abinary array for decoding the digital data decoded by the Viterbidecoder into one of the N legal codes; a delay device, coupled to theoutput of the ADC, for delaying the data stream, and then outputting adelayed data stream corresponding to the data stream; a reference leveladjusting device, respectively coupled to an output of the Viterbidecoder and an output of the delay device, for receiving the coderelative to the data stream and the delayed data stream corresponding tothe code relative to the data stream, adjusting the N reference levelsin accordance with an algorithm including a conversion-speed-adjustingcoefficient, and outputting the N reference levels to the Viterbidecoder; a conversion-speed-adjusting coefficient generating device forgenerating the conversion-speed-adjusting coefficient in response to atleast one condition signal, and outputting theconversion-speed-adjusting coefficient to the reference level adjustingdevice; at least one condition detector which each is in charge ofdetecting a respective condition associated with the retrieved signaland outputs one of the at least one condition signal corresponding tothe detected condition to the conversion-speed-adjusting coefficientgenerating device; and a default reference level enabling device, forgenerating a default reference level enabling signal in response to theat least one condition signal, outputting the default reference levelenabling signal to the reference level adjusting device, wherein whenthe reference level adjusting device receives the default referencelevel enabling signal, the reference level adjusting device loads adefault reference level corresponding to the default reference levelenabling signal as an initial value.
 19. In an optical informationreproducing system, a decoding apparatus for decoding a signal retrievedby said system from an optical information recording medium, N legalcodes being predetermined, wherein N is a natural number, said decodingapparatus comprising: an Analog-to-digital converter (ADC) forconverting the retrieved signal into a data stream; a digital equalizer,coupled to an output of the ADC, outputting an equalized data streamcorresponding to the data stream; a Viterbi decoder, coupled to anoutput of the digital equalizer, for decoding, according to N referencelevels and a level of the equalized data stream, the equalized datastream into a digital data, wherein each of the N reference levelscorresponds to one of N legal codes; a binary array for decoding thedigital data decoded by the Viterbi decoder into one of the N legalcodes; a delay device, coupled to the output of the digital equalizer,for delaying the equalized data stream, and then outputting a delayeddata stream corresponding to the equalized data stream; a referencelevel adjusting device, respectively coupled to an output of the Viterbidecoder and an output of the delay device, for receiving the coderelative to the equalized data stream and the delayed data streamcorresponding to the code, adjusting the N reference levels inaccordance with an algorithm including a conversion-speed-adjustingcoefficient, and outputting the N reference levels to the Viterbidecoder; a conversion-speed-adjusting coefficient generating device forgenerating the conversion-speed-adjusting coefficient in response to atleast one condition signal, and outputting theconversion-speed-adjusting coefficient to the reference level adjustingdevice; and at least one condition detector which each is in charge ofdetecting a respective condition associated with the retrieved signaland outputs one of the at least one condition signal corresponding tothe detected condition to the conversion-speed-adjusting coefficientgenerating device.
 20. In an optical information reproducing system, adecoding apparatus for decoding a signal retrieved by said system froman optical information recording medium, N legal codes beingpredetermined, wherein N is a natural number, said decoding apparatuscomprising: an Analog-to-digital converter (ADC) for converting theretrieved signal into a data stream; a digital equalizer with anadjustable coefficient, coupled to an output of the ADC, outputting anequalized data stream corresponding to the data stream; a Viterbidecoder, coupled to an output of the digital equalizer, for decoding theequalized data stream into a digital data; a binary array for decodingthe digital data decoded by the Viterbi decoder into one of the N legalcodes; a delay device, coupled to the output of the ADC, for delayingthe data stream, and then outputting a delayed data stream correspondingto the data stream; a reference signal generator, coupled to an outputof the binary array, for generating a reference signal by use of thecode decoded by the binary array; an error calculator, respectivelycoupled to an output of the reference signal generator and an output ofthe digital equalizer, for generating an equalized error signal; anadjusting device, coupled to an output of the error calculator and anoutput of the delay device, for adjusting the adjustable coefficient forthe digital equalizer in accordance with an algorithm including aconversion-speed-adjusting coefficient; a conversion-speed-adjustingcoefficient generating device for generating theconversion-speed-adjusting coefficient in response to at least onecondition signal, and outputting the conversion-speed-adjustingcoefficient to the adjusting device; and at least one condition detectorwhich each is in charge of detecting a respective condition associatedwith the retrieved signal and outputs one of the at least one conditionsignal corresponding to the detected condition to theconversion-speed-adjusting coefficient generating device.
 21. In anoptical information reproducing system, a decoding apparatus fordecoding a signal retrieved by said system from an optical informationrecording medium, N legal codes being predetermined, wherein N is anatural number, said decoding apparatus comprising: an Analog-to-digitalconverter (ADC) for converting the retrieved signal into a data stream;a Viterbi decoder, coupled to an output of the ADC, for decoding thedata stream into a digital data in accordance with N reference levelsand a level of the data stream, wherein each of the N reference levelscorresponds to one of N legal codes; a reference level adjusting device,for adjusting the N reference levels, and outputting the N referencelevels to the Viterbi decoder; and a detecting device, for detecting acentralization of the N reference levels; wherein the centralization ofthe N reference levels is used to indicate a quality of the retrievedsignal.
 22. In an optical information reproducing system, a decodingapparatus for decoding a signal retrieved by said system from an opticalinformation recording medium, N legal codes being predetermined, whereinN is a natural number, said decoding apparatus comprising: anAnalog-to-digital converter (ADC) for converting the retrieved signalinto a data stream; a Viterbi decoder, coupled to an output of the ADC,for decoding the data stream into a digital data in accordance with Nreference levels and a level of the data stream, wherein each of the Nreference levels corresponds to one of N legal codes; a reference leveladjusting device, for adjusting the N reference levels, and outputtingthe N adjusted reference levels; a reference level setup device,outputting N reference levels which each has a respective setup value;and a reference level selecting device, for receiving the output of thereference level setup device and the output of the reference leveladjusting device, and alternatively outputting the output of thereference level setup device or the output of the reference leveladjusting device to the Viterbi decoder.